On Thursday, Citi (C) reported that earnings in the first quarter were up 20% from a year ago, to $4.8 billion. That eclipsed the $3.4 billion that rival Bank of America earned in the same time. And it was better than analysts had predicted. On a per share basis, Citi earned $1.51, which beat analysts estimates of $1.39 a share. Investors seemed pleased with the results. Citigroup’s shares were up nearly 2% at mid-day on Thursday.

What you need to know: While Citi’s earnings were up, not all of its businesses were. Profits in its investment bank were basically flat from a year ago. And the bank’s overall revenue was down 2% from 2014.

The biggest drop came from Citi’s troubled Latin American business, where the bank has run into regulatory issues in Mexico as part of a bribery scandal, and where it is embroiled in the fight between Argentina and its hedge fund bond holders. Business in that area was down 12% in the first quarter. Citi recently named one of its well-regarded executives, Jane Frazer, to take over the business in the region, where Citi has traditionally done well.

Consumer banking revenue was down too, by 2%. Low interest rates have made lending less profitable. Brian Kleinhanzl, an analyst at KBW, called the quarter “clean,” which is not the biggest compliment.

The big number: What really drove up Citi’s bottom line was cost cutting. Expenses at Citi were down 10% from a year ago and 25% less than what they were just three months before, during the last quarter of 2014. Corbat prides himself on his ability to reduce expenses and run Citi efficiently. Citi cites its efficiency ratio (expenses/revenue – the lower the figure the better) of 54% at the top of its earnings press release. It is one of the lowest ratios on Wall Street.

And, at least on the cost cutting front, Corbat has excelled. The year before Corbat became CEO, Citi’s expenses, including credit losses, were roughly $71 billion. He now runs the same bank, generating roughly the same in revenue, for $20 billion less than his predecessor, Vikram Pandit.

What you may have missed: Citi’s investment bank, after being nearly cast off after the financial crisis, has been showing signs of life recently. That didn’t continue in the quarter. Revenue from underwriting stock and bond deals and advising on mergers was up 14%. But bond trading, which generates more than a third of the Citi’s investment banking revenue, fell 11%. Stock trading revenue was also down 1%.

The investment banking results come at an odd time for Citi’s top management. In a shuffle, Corbat recently elevated Jamie Forsee, the bank’s head of investment banking, to the role of Citi’s sole president. That makes Forsee the most obvious successor to Corbat, who just a few weeks ago, on the verge of the latest Fed bank stress test, looked like he might be out the door. Citi’s first quarter results aren’t a great coming out party for Forsee, but perhaps that’s what makes him an attractive No. 2 for Corbat. Citi passed the stress test, and earnings are up. So, for now, investors again seem pleased with Corbat. But if growth doesn’t eventually show up, investors could again start looking around for a replacement.